Chemical vapor deposition (CVD) is a process for forming a material layer on a substrate by the reaction of gas phase reactants at or near a substrate surface. Vacuum processing chambers are generally used for CVD and etching of materials on substrates by supplying process gas to the vacuum chamber and applying a radio frequency (rf) field to the gas. Examples of parallel plate, transformer coupled plasma (TCP.TM., also called inductively coupled plasma or ICP), and electron-cyclotron resonance (ECR) reactors are disclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; and 5,200,232. The substrates are held in place within the vacuum chamber during processing by substrate holders. Conventional substrate holders include mechanical clamps and electrostatic clamps (ESC). Examples of mechanical clamps and ESC substrate holders are provided in commonly owned U.S. Pat. No. 5,262,029 and commonly owned U.S. application Ser. No. 08/401,524 filed on Mar. 10, 1995. Substrate holders in the form of an electrode can supply rf power into the chamber, as disclosed in U.S. Pat. No. 4,579,618.
Plasma processing systems wherein an antenna coupled to an rf source energizes gas into a plasma state within a processing chamber are disclosed in U.S. Pat. Nos. 4,948,458; 5,198,718; 5,241,245; 5,304,279; and 5,401,350. In such systems, the antenna is located outside the processing chamber and the rf energy is supplied into the chamber through a dielectric window. Such processing systems can be used for a variety of semiconductor processing applications such as etching, deposition, resist stripping, etc.
Thermal CVD processes typically rely on heating of the substrate surface in order to promote the reaction(s) which result in formation of compound(s) on the substrate surface. Conventionally, the substrate surface is heated by applying an rf bias voltage to the substrate. The use of the rf bias voltage to heat a substrate to promote the reactions generates a DC bias in the plasma near the surface of the substrate. This DC bias accelerates ions toward the substrate surface, and the ensuing collision of the ions transfers energy to the substrate, thereby heating the substrate.
A problem with this conventional heating of the substrate surface with an rf bias voltage is that it causes sputtering of the material on the substrate due to ion bombardment. This can cause damage to the substrate surface. Various gases have been used as the reacting gases in an attempt to lessen the sputtering while heating the substrate with the rf bias voltage. The problem of sputtering remains, however.
Other methods of heating the substrate surface have also been proposed, including heating lamps, resistor heaters, and other in-situ substrate heating methods. These methods are limited by slow response time and process variability due to previous processing of the substrate or the condition of the substrate.
There is thus a need for a method for minimizing sputtering during heating of a substrate surface for processing such as CVD processing.